Stephens story is in Acts 7. Paintings of his martyrdom are not common by any means, but this and the later one at Catfield in Norfolk (link below) have survived. Even in the paintings faded state, enough can be seen of his robes to confirm that he is correctly dressed as a deacon of the church as he kneels facing right in prayer. The legs of a torturer are still just visible to the right, but the other torturer on the left, about to hurl a stone, is fairly clear in his entirety. He has a great bag of stones, all of more or less uniform size and shape as was apparently prescribed, slung around his waist¹. He also has interesting hair - a shock of it standing out around his head, especially on the left. Bad characters in medieval narrative painting often have wild hair - Cains, in a painting of Cain and Abel at nearby Kelmscott and roughly contemporary with this, is similar.
Some other paintings at Black Bourton are in the table below. There are more, including the Coronation of the Virgin, the Adoration of the Magi and the Baptism of Christ all of the same 13th century date.

¹Or, alternatively, holds the stones in the tucked-up lap of his outer garment.